mattallac

iTrader: (7)

Has anyone done it ? They are 32mm each and should be easy to fit on a rotary in any rx engine bay . I know they install at a 20 or so degree tilt that helps even more on fitment . I have not started to make a manifold yet but I would appreciate any thoughts ( good or bad ) thanks for reading

peejay

32mm is way too small for a rotary, I'd think.

The SMALLEST 4 throttle setups I have ever heard of are 36mm. The most common were the dual 40 DCOE setup and racers would bump up to 45 DCOEs!

RXBeetle

Unless the plan is to run all 4 carbs, then the venturi diameter are similar to a 600cfm holley. I've heard slide carbs are a bitch to jet. I'm guessing it would be a mile off coming off a <100hp bike.

WANKfactor

iTrader: (1)

Ok im the furthest thing from a carb tuner you can get but if you crunch the numbers, 4x32mm carbs has the crossection of 2x45mm carbs.
Not only that, a four piston 4 stroke engine has 1 firing event per revolution, so 1 pulse per carb every 4 revolutions,
Whereas a 2 rotor engine has 2 pulses per revolution, effectively doubling the carbs flow capacity. 100hp wirth of carbs becomes 200hp.
Depending what bike they are off will be able to support much more than that, 600 bikes rom 30 years ago were making 130, and flatsides usually add quite a lot of extra power potential on top of that.

peejay

It doesn't really work that way, though. The problem is, the 4x32s have a whole lot more surface area than the 2x45s, and that surface area equals dead flow and resistance to motion. 4x40mm is about equal to a single 48 IDA even though it has much more theoretical cross section.

Also, a 45mm DCOE is small. Feels just like a stock Nikki. (IIRC the Nikki's venturi and bore area is roughly equal to that of a 48 IDA! Surface area losses are a real thing)

mattallac

iTrader: (7)

So from what I found they are 39 mm , I’m gonna get a set to get some measurements. I would be running 4 carbs . My 13b street port runs a Weber 48 ida w/42mm choke tubes . It seems the flat slide carbs I’m looking at can be limited by velocity stack size . (33mm,37mm50mm) I would think this would work and I appreciate the feed back . I got this idea by an au. Guy using 4 individual throttle bodies on his motor . I also think they make float bowl extensions for these carbs . The carbs I’m looking at are a flat slide only , not a “cv”carb running on vacuum.

WANKfactor

iTrader: (1)

^i thought you had a set lying around. Thats a pretty expensive experiment. Could probably go ida injection for the same money.

mattallac

iTrader: (7)

Nope , ida injectors from start to finish is about 3000.00 start to finish not including tune . The carbs I’m looking at are to an old gsxr 1100 . Guys want 600-800 for them but I’m sure I can find them for a few hundred $ . A manifold would be easy to fabricate .
My point to all of this is to find out what mm size would give you the right amount of air per runner and how much better or worse would it work . We have all seen side draft manifolds for Weber/ Mikuni that don’t fit on any rx7 model (maybe Repu). I always wondered how they worked . This would be a more compact setup . I’ve owned every rotary carb setup ( dcd,ida,idf,4barel and dcoe w/180 degree runner )except a direct side draft .

peejay

The side draft manifolds fit RX-7s... I've driven them. You just need to use an air cleaner that is relatively short.

You also need to use shorter velocity stacks. I forget the exact details, but there is a rumor that the flat manifolds really screw with the jetting compared to a wraparound. Well that is true if you keep the tall velocity stacks so that they are 1/2" away from the air cleaner cover. That isn't a manifold problem, it's an installation error.

chuyler1

iTrader: (1)

I'll chime in and confirm 4x32 as well as 2x45 is simply too small for a 13b if you are trying to make more power than stock. 2x45 is too small for a streetport 12a as I have recently learned, maxed out at 130hp. The dyno might have been reading low that day, but the builder says port job should have made 160-170 with a 48IDA. It might have gotten there but power dropped at 7k RPM no matter how short we went on velocity stacks. I wanted it to be a bit more torquey so I was trying the wrap-around manifold. I've since switched to the non-wrap-around manifold but haven't been back to the dyno.

fidelity101

iTrader: (11)

or cut the oil filler tube and re-weld it shorter. thats what I did when I ran a DCOE style. I had 4-6" long horns on it.

peejay

Not that type... this type:



Oddly enough I have one of these but can't use it because the Dell'Orto accelerator pump arm interferes with the exhaust manifold, and I don't want a header on what is supposed to be a pleasant car.

chuyler1

iTrader: (1)

This is pleasant to drive, even with a light flywheel and big street port.

fidelity101

iTrader: (11)

Actually I'm mulling the idea of grafting a hayabusa ITB setup to a custom 3d printed aluminum lower intake manifold. they are x4 45mm throttles...